The goal of the proposed research is to determine the potential clinical utility and significance of evoked oto-acoustic emissions. Evoked emissions appear to be closely linked to non-linear, frequency-selective elements within the cochlea. In addition, they are highly sensitive to cochlear status and can be altered easily by such metabolic and traumatic insults as intense sound exposure, ototoxic drugs and anoxia. These characteristics of evoked emissions suggest that they are a potential non-invasive tool for assessing cochlear status in humans. The proposed research will provide a systematic set of data on the input-output relations among evoking stimuli and evoked oto-acoustic emissions from large numbers of normal and non-normal human ears. These data will provide a basis for evaluating the clinical applicability of emissions. The proposed research will also provide insight into the source and/or mechanisms involved in the generation of emissions, as well as insight into alterations in cochlear status such as permanent sensorineural hearing loss, Meniere's disease, ototoxic drugs and intense noise exposure. A unique feature of the proposed research is the application of signal analysis techniques that have been used in other fields (e.g. sonar, radar, radiology, geophysics) where recovery of low-level signals embedded in noise is also a goal to the measurement and analysis of evoked oto-acoustic implemented in such a way as to be clinically accessible.